Restorative dental work includes making a replica tooth. The replica tooth is made based on the tooth to be restored. A traditional method of creating a replica tooth is to apply a pliable molding material around the tooth to be replaced. The cavity formed in the molding material by the tooth to be replaced can then be used to create a replica tooth of the desired dimensions and shape. More recent dental restoration techniques, however, utilize computer-aided methods.
In order to capture a computer image of the tooth by an imaging device, the tooth is made to contrast with the rest of the patient's mouth by coating the surface of the tooth (also referred to as the dental site) with a suitable powder. This step is known as “powdering” the tooth. Suitable powders include contrast mediums such as titanium dioxide (TiO2).
The contrast medium provides a means by which an infrared camera can photograph and digitize the tooth to be restored. The replica tooth is then designed through the use of a computer. For example, imaging systems such as the system manufactured by Siemens Dental Products Division and distributed in the United States by Patterson Dental Supply, Inc. of St. Paul, Minn. under the name CEREC III include a handheld infrared camera as well as a computer that converts the recorded reflected infrared image of the tooth into values representative of the height and depth of the surface of the tooth. This renders a virtual model of the tooth image that can be utilized to design a virtual restoration for the tooth. Once the design of the replica tooth is completed, the dentist utilizes a milling machine for cutting the actual replica tooth from a ceramic block.
An important tool used with computer-aided dental restoration techniques is a powdering device (also referred to as a dental powder applicator). The powdering device is important because powdering is the first step towards successful completion of restorative dental work. Problems with powdering devices, however, such as clogging, moisture contamination of the imaging powder and limited range of use interfere with the attainment of acceptable results during imaging and digitizing of the dental site. For example, the imaging process requires the application of a uniform coat of powder so that the entire intended dental site is covered. Too much powder is a problem as is too thin a coat. Thus, it is important to have a system and method capable of applying a uniform coat of powder to the dental site.
Existing powdering systems have attempted to overcome these problems with limited success. An early powdering device involved a first container holding pressurized butane gas and the second container holding the contrast medium. The device operated by releasing butane from the first container into the second container. The butane then carried contrast medium out of the second container and through a flexible tube towards the tooth to be coated. Vita Zahnfabrik H. Rauter Graph And Co. KG of Bad Sackingen, Germany distributed such an applicator. Alternative suppliers of the butane propellant devices included IVOCLAR (sold as ProCad powder) and VITA brand contrast medium.
Existing powdering systems, including the butane propellant device, require additional preparation steps such as applying imaging liquid with a brush to all the surfaces visible in the imaging step and blow drying these surfaces after application of the imaging liquid. Following these preparation steps, the dental powder was sprayed on in a steady stream from a nozzle held about one or two centimeters from the tooth surface. Difficulties were encountered with the butane propellant device, however, when trying to achieve uniform and even application of the powder in remote locations of the mouth. For instance, in many cases the patient's cheek is in the proximity of the side of the tooth and thus must be forced outwardly therefrom in order for the powder to be sprayed evenly on the side of the tooth. Because the butane propellant device uses an outlet stem that bends when contacted against the cheek, the user of the device had to force the cheek away using a second hand or additional device, which added further complexity to the powdering process.
An alternative device is described in U.S. Pat. Nos. 5,944,521 and 6,099,306 entitled Tooth Powdering Applicator (the Lawler device). The Lawler device replaces the attached container of pressurized butane with a connection to a pressurized fluid. The outlet tube is rigid and curved. The Lawler device allows a dentist to use a single hand to hold the device and simultaneously rotate the outlet tube without use of the dentist's second hand. The stated advantage of the Lawler device was that the outlet tube could be rotated to allow the discharge stream from the powdering device to be aimed at various tooth surfaces without having to tilt the powder reservoir. Tilting the powder reservoir in the powdering device, however, leads to sporadic powder flow, clumping of the powder and ultimately clogging of the powdering device. A device based on the Lawler patent is sold under the name POWDERMEISTER by Powder Meister, Inc. of Bloomington, Ind.
Despite the purported advantages of the Lawler device, the powder reservoir of the POWDERMEISTER device must still be held in an upright or vertical position to allow the powder to enter the airstream. Some powder clumps are also attributed to storing the POWDERMEISTER on its side or upside down so that excess powder enters the powdering tube. Water in the pressurized source of air poses a further problem with the POWDERMEISTER as the water will cause the powder to clump. An additional problem with the POWDERMEISTER device is introduced by a thumbscrew controlled air valve on the container. The amount of powder applied to the tooth is very sensitive to the position of the thumbscrew. That is, very little movement of the thumbscrew is needed to effect a change in the powder flow. Some dentists find that thumbscrews turn too freely.
Another alternative powdering device is disclosed in U.S. Pat. No. 6,416,322 to Qualliotine et al. (the Quallitone patent). A device based on the Quallitone patent is sold under the name POWDERPERFEKT by Ourglass Ltd. of Greenville, N.C. The POWDERPERFEKT device states several objects including providing a device that eliminates powder clumping caused by moisture in the pressurized air supply. Despite this, the POWDERPERFEKT design is still prone to clogging for several reasons.
First, there is a 90-degree bend that the fluidized contrast medium must take prior to exiting the apparatus. The velocity of the contrast medium impacts upon the 90-degree bend causing a deposition of powder that blocks the air passage. This is also true of the butane propellant device and the POWDERMEISTER device.
Second, the POWDERPERFEKT device depends upon the pressurized air line to be dry between the air compressor and desiccant only and does not address the need for keeping the powder dry between uses or ensuring that the air supply is dry prior to contact with the dental powder.
Third, as with the butane propellant device and the POWDERMEISTER device, the powder container must have a sufficient level of dental powder to ensure that the dental powder is sufficiently fluidized. This is because the design of the POWDERPERFEKT device directs the path of air down into the powder where it disperses and aerolizes the dental powder inefficiently by causing large drifts of the dental powder to form necessitating physical agitation or tapping of the powder container to keep the powder in the path of the air stream. The powder then must travel up into the 90-degree bend turn prior to exiting the device. There is also a large discrepancy between the volume of gas and fluidized material in the powder container and the small orifice that it exits. This discrepancy leads to an abrupt change in velocity of the powder stream resulting in clogging. Finally, there are limitations respecting angles that the disclosed device can be tilted during use before the dental powder jams. The same is true for the POWDERMEISTER device.
Fourth, the intrinsic nature of the air control button to initiate the powder flow is too course to allow sufficient fine control of the airflow. Thus, the air pressure flowing through the powder chamber is high and not adjustable, which leads to excessive powder application.